Piezoelectric ceramic composition



Get. 27, 1970 KYQHEI MURAKAwA ET AL j 3,536,625

PIEZOELECTRIC CERAMIC COMPOSITION Filed oct. 25, 1967 4 Sheets-Sheet 1 Pb Ti 0 Pb Zr o =o.55 0.45

PLANAR COUPLING FACTOR(kp) U! o a s a I I l I I l I I IO 20 3o 40 so so 10 so 90 I00 FIGJ Pb(MgW) O (MOL%) 2 Pb Zy0 A )mvvumv gunman CR YS TAL PHASE-F|G 3-\ D---- PSEUD CUBIC O- TETRAGONAL O---- RHOMBOHEDRAL A AVQVAVAWA AVAYAVAYAYAVA AYAYAVAVAVAVAA Oct. KYOHEl MURAKAWA ET AL 3,536,625

PIEZOELECTRIC CERAMI C CUMIOS lllON Filed Oct. 25, 1967 I 4 Sheets-Sheet :3

PLANAR COUPLING FACTOR (NON ADDITIVE) kp.

Pb Zr 0 PbTiO f xloo TABLE 3 H20 C Z NO l6 W M TKLE 3 -40 2O 0 2O 4O 6O 80 T (TEMPERATURE C) TEMPERATURE CHANGE IN RESONANT FREQUENCY FIG.8

7, 1970 KYOHEI MURAKAWA ET AL 3,536,625

PIEZOELECTRIC CERAMIC COMPOSITION Filed Oct. 25, 1967 4 Sheets-Sheet 5 DIELECTRIC PROPERTIES FIG.5

Oct. 27, 1970 KYOHEl u w ETAL 3,536,625

PIEZOELECTRIC CERAMIC COMPOSITION Filed Oct. 25, 1967 4 Sheets-Sheet L CURIE POINT D DIELECTRIC CON NTS PbTiO FIG .7

Pb Ti0 I Pb(MgW) O NA OUPLING OR I Mg O -Pb Ti Pb 3 FAMILY United States Patent 01 3,536,625 Patented Oct. 27, 1970 ice US. Cl. 252-623 2 Claims ABSTRACT OF THE DISCLOSURE Described is a three component piezoelectric ceramic composition of (Pb(Mg-W) O (PbTiOg) and (PbZrO having the composition of the range contained in polygon ABCDEFGA in the triangular composition diagram shown in FIG. 2 wherein Pb (Mg-OM20; PbTiOa PbZI'O 0. 05 0. l5 0. 80 0. 05 0. 35 0. 60 0. 05 0. 55 0. 40 0. 05 0. 80 0. l5 0. 0. 80 0. l0 0. 80 0. 10 0. l0 0. l0 0. 10 0. 80 0. 05 0. 0. 80

and containing as additives at least one member of the group consisting of iron oxide, chromium oxide, manganese oxide, lanthanum oxide and niobium oxide in an amount of from 0.1 to 2% by weight, together with 0.02 to 0.5% by weight of silicon dioxide.

Our invention relates to piezoelectric ceramic compositions and a method of manufacturing the same.

Well known piezoelectric ceramics such as, for example, barium titanate ceramics (BaTiO and lead titanate-zirconate ceramics (Pb(TiZr)O or PbTiO PbZrO are utilized as various kinds of electromechanical transducers by applying DC electric field to them and polarizing them, causing them to have piezoelectric properties. These piezoelectric ceramics are utilized, for example, as acoustic transducers in pickups and microphones, ultrasonic resonators, so-called mechanical filters and intermediate frequency transformers of 455 kc. The main object of our invention is to provide piezoelectric ceramics that can be utilized as mechanical filters or ceramic filters of high performance, but, needless to say, these ceramics can also be utilized as the other devices described above.

Our invention relates to the lead magnesium tungstate/ lead titanate/lead zirconate system which is a new piezoelectric ceramic, and to an additive that can effectively improve the electromechanical properties, and to an additive that can also improve the temperature characteristic.

In the drawings,

FIG. 1 shows the variation of the planar coupling factor (kp) when Pb(Mg-W) O is added to a composition of PbTiO' of 0.55 mol and PbZrO of 0.45 mol.

FIG. 2 is a triangular composition diagram showing the rangeof eifect of this invention, wherein the range contained in a polygon of ABC-DEFGA shows the limit in which the effect is excellent and BCKJIHB shows the preferred range in which the electromechanical property is excellent.

FIG. 3 is a triangular composition diagram showing the distribution of the crystal phase, by X-ray diffraction, of three component piezoelectric ceramic according to our invention.

FIG. 4 is a triangular composition diagram showing the distribution of the electromechanical coupling coefiicient of three component piezoelectric ceramic according to our invention.

FIG. 5 shows an example of the dielectric properties in 1 kc. of three component piezoelectric ceramic according to our invention.

FIG. 6 is a triangular composition diagram showing the distribution of the dielectric properties of three component piezoelectric ceramic according to our invention and the distribution of the Curie point and the dielectric constanttl kc.).

FIG. 7 is a triangular composition diagram showingthe distribution and range of the electromechanical coupling coeflicient of three component piezoelectric ceramic according to our invention to which MnO or Fe O has been added.

FIG. 8 shows an example of the temperature characteristic of the resonance frequency of three component piezoelectric ceramic according to our invention utilized as a resonator.

It is generally known that, when an anti-ferroelectric substance and a ferroelectric substance that are similar to each other in structure are solved into a solid solution, ferroelectricity is exhibited. For example, a solid solu tion (what is called a ceramic) consisting of lead titanate and lead zirconate is an excellent ferroelectric substance and an excellent piezoelectric ceramic. Lead titanate is a ferroelectric having the perovskite-type structure and lead zirconate is an anti-ferroelectric having the similar structure. However, when lead zirconate and lead titanate above several mol percent are solved into a solid solution, the lead zirconate is converted into a ferroelectric. This was reported in 1952 by G. Shirane, K. Suzuki and A. Takeda in Journal of the Physical Society of Japan, vol. 7, No. 12, 1952.

The present inventors utilized the same phenomenon between lead magnesium tungstate and lead titanate. It was reported by G. A. Smolenskii, A. I. Agranouskaya and V. A. Isupov in Fizirka Tuerdogo Tela, vol. 1, 990, 1959 that lead magnesium tungstate (Pb(Mg-W) O is an anti-ferroelectric having the perovskite-type structure and its Curie point is 40 C. When lead magnesium tungstate and lead titanate are solved into a solid solution, ferroelectricity is exhibited and piezoelectricity also increases greatly. When lead magnesium tungstate of 50 mol percent and lead titanate of 50 mol percent were solved into a solid solution, an excellent ceramic could be obtained and when said ceramic was polarized by a strong DC electric field, an electromechanical coupling factor of 15-20% could be obtained.

This ceramic, however, was still unsatisfactory for practical use as a piezoelectric element. We therefore improve the characteristic by further solving lead zirconate to obtain extremely excellent results. For example, when a three component solid solution consisting of 15 mol percent lead magnesium tungstate (Pb(Mg-W)1 2O3), 45 mol percent lead titanate (PbTiO and 40 mol percent lead zirconate (PbZrO was polarized by a DC electric field of 40 kv./cm., the electromechanical coupling coefiicient (planar coupling factor) was 0.40 and the mechanical Qm as a resonator was 300.

The electromechanical coupling coefficient and the Qm were calculated approximately in the following manner by the constant-current method.

kp =2.51 fl expressed by the value of kp 100 when expressed by percent X f f i f 2 Qm =100 kp=0.30

Here,

fa=anti-resonance frequency fv=resonance frequency kp=planar coupling factor (electromechanical coupling factor in the radial direction) Qm=quality of resonance I 1 frequency 3 db higher than fr.

The generally known solid solution of lead titanate and lead zirconate is an excellent piezoelectric material. It is, however, difiicult to manufacture this kind of solid solution since much of the lead oxide evaporates in the manufacturing process. However, it is very easy to make a solid solution of lead titanate and lead zirconate. And when a minute amount of additive is added, the additive is ordinarily diffused by interstitial diffusion.

Based on the same idea, an excellent result cannot be obtained when a three component ceramic of lead magnesium tungstate/ lead titanate/lead zirconate is manufactured. For example, when lead magnesium tungstate of 0.5% by weight, 1% by weight, 5% by weight or by Weight is added to a two component ceramic consisting of lead titanate and lead zirconate and this is fired, the characteristic of the resultant ceramic was greatly lower than the characteristic of the two component system. The characteristics become equal to that of the two component system only when more than 10% of the lead magnesium tungstate is present.

From the above phenomenon it is seen that in the initial stage of the interstitial diffusion of the additive, the piezoelectric properties of the lead titanate and lead zirconate are disturbed and the characteristic of the ceramic is lowered. When the amount of additive has become suificiently great, a unique structure is constructed and the piezoelectric property is recovered. The piezoelectric property is greatly affected by distortion of the crystal structure. From this phenomenon it becomes apparent that we have formed a completely new three component ceramic rather than improved the two component of lead titanate and lead zirconate.

FIG. 1 shows how the electromechanical coupling coefficient varies when lead magnesium tungstate is added to a two component ceramic of 0.55 mol lead titanate and 0.45 mol lead zirconate.

It can be considered that the three component system ceramic of lead magnesium tungstate, lead titanate and lead zirconate is formed by reaction whereby lead zirconate is diffused by interstitial diffusion into a two com ponent system ceramic of lead magnesium tungstate and lead titanate. Lead magnesium tungstate and lead titanate react at a lower temperature, i.e., at about 1000-1100 C. and, therefore, at the temperature of 1250-1300 C. at which lead zirconate reacts, the lead magnesium tungstate/ lead titanate melt becomes porous whereby a ceramic of high density cannot be obtained. For this reason, in order to obtain excellent three component ceramics of high density which is the object of this invention, it is necessary to first cause lead magnesium tungstate and lead titanate to react with each other at a lower temperature to thereby form a ceramic and then slowly diffuse lead TABLE 1 Pb(Mg-W)1/2O PbTlOs (mol.)

As the result of a further crystallographical investigation by X-ray diffraction, the tetragonal phase and the rhombohedral phase are shown in FIG. 3. By comparison of FIG. 4 with FIG. 3 it is seen that the piezoelectric property is most improved around the boundary between the two phases. The pseudo-cubic phase is not ferroelectric but is an area that can be utilized piezoelectrically.

Furthermore, an advantage of the three component ceramic of lead magnesium tungstate, lead titanate and lead zirconate in accordance with this invention as an electromechanical transducer is that the resonance is excellent when oscillated, that is, an excellent resonance can be obtained and Qm can be made large when the ceramic is applied to a mechanical filter.

When the electromechanical coupling coefiicient of a two component ceramic of lead titanate and lead zirconate and the electromechanical coupling coefficient of the three component ceramic according to our invention are nearly equal, the mechanical Qm of the latter is nearly twice as large as that of the former.

The electromechanical coupling coefficient and the mechanical Qm are inversely related and if one is made large, the other becomes small naturally, wherefore if only the electromechanical coupling constant is noted, the planar coupling factor can amount to 50%60%.

These constants are ordinarily utilized for judging the performance when the piezoelectric materials are used as mechanical resonators or electromechanical transducers. Various kinds of applications are also often determined by these constants. For example, when the piezoelectric materials are used as pickups, microphones and ultrasonic resonators, the electromechanical coupling coetficient must be made large whereas when said materials are used as mechanical filters and the like, the mechanical Qm must be made large. In these cases, it is most convenient to change the electromechanical coupling factor and the mechanical Qm according to the purposes of use by adding additives to the materials.

Another object of our invention is to provide the most efiective additive for the three component piezoelectric ceramic of lead magnesium tungstate, lead titanate and lead zirconate.

In general, the factor for enlarging the mechanical Qm and the factor for enlarging the electromechanical coupling coefficient are exactly reverse to each other. If the mechanical Qm is made large, the electromechanical coupling factor becomes small necessarily while, adversely, if the electromechanical coupling coefficient is made large, the mechanical Qm becomes small. Namely, a material with a large mechanical Qm has a large Youngs modulus and small Poissons ratio and is rigid and fragile whereas a material of a large electromechanical coupling factor has a relatively small Youngs modulus and a large Poissons ratio. Thus, it is apparent that the mechanical Qm and the electromechanical coupling coefiicient are inverse to each other.

For this reason, it is necessary to select additives corresponding to the purposes of use of the ceramic. We have added various kinds of metal oxides to the three component ceramic consisting of lead magnesium tungstate, lead titanate and lead zirconate and investigated the electromechanical properties, and, as the result, have found that iron oxides, manganese oxides and chromium oxides reduce the Poissons ratio and increase Youngs modulus, thus increasing the mechanical Qm, and that rare earth metal oxides represented by lanthanum oxides and niobium oxides increase Poissons ratio and reduce Youngs modulus, whereby materials. of large electromechanical coupling coefiicient can be obtained.

We have further found that silicon dioxide (SiO plays an important part as a second additive. That is, by adding the proper amount of silicon dioxide to the abovementioned various kinds of metal oxides, the mechanical Qm can be further enlarged and the electromechanical coupling coefficient can also be greatly improved. For example, when percent wt. Fe O is added to a combination of Pb(Mg-W) O of 0.15 mol, PbTiO of 0.40 mol and PbZrO of 0.45 mol, the mechanical Qm becomes 1300 and the planar coupling factor (kp) becomes 36% whereas when 0.02-05 wt. percent silicon dioxide is also added, Qm becomes 1500 l700 and kp becomes 40%.

A further object of our invention is to improve the temperature characteristic of the resonance frequency and the secular variation. Chromium oxide, from the metal oxides as above described, greatly improves the temperature characteristic of the resonance frequency. However, when chromium oxide is coexistent with iron oxide or manganese oxide, the electromechanical property is also greatly improved, wherefore a piezoelectric element having a particularly excellent stability can be obtained. Details of this point will become apparent from the description of specific embodiments hereinbelow.

EXAMPLES An example of the method of manufacturing lead magnesium tungstate is as follows. First of all, 446.42 g. lead oxide (PbO), 249.9 g. tungstic acid (H WO or 231.9 g. tungsten trioxide (W0 and 40.3 g. magnesium oxide (MgO) were well ground and mixed in a mortar or the like. These were then placed in an alumina ceramic crucible and calcined for an hour at a temperature of 900 C. Thus, a yellow solid lead magnesium tungstate (Pb(Mg-W) O ceramic was obtained.

Next, a method of manufacturing lead titanate will be described. 223.21 g. lead oxide (PbO) and 79.9 g. titanium oxide (TiO of a purity of above 99.8% were well ground and mixed in a mortar or the like and were then put in an alumina ceramic crucible and were calcined for an hour at a temperature of 900 C. Thus, a light yellow green lead titanate (PbTiO was obtained.

Lead zirconate was produced by grinding together 223.21 g. lead oxide (PbO) and 123.22 g. zirconium oxide (ZrO of a purity of about 99.5% in a mortar or the like. These were then placed into an alumina ceramic crucible and calcined for an hour at a temperature of Mol Grams Pb(Mg-W)i/2O3 53. PbTlO; 136. 40 PbZrOa 138. 57

The Pb(MG-W) O PbTiO and Pb ZrO were well mixed and ground for several hours in a mortar of alumina, ceramic or agate under a dry atmosphere, and after being reduced to corpuscles under 1 micron, they were placed into a suitable mold and molded under a pressure of 0.5-1.0 ton/cm. The compact formed was taken out of the mold and placed into a crucible or a boat and fired. Here it is not necessary to take the evaporation of lead oxide (PbO) into consideration. Such particular consideration as was required in the two component system of lead titanate (PbTiO and lead zirconate (PbZrO is not necessary in this case. The firing condition was as follows. The molded material was first heated slowly for 3 hours at a temperature of 1100l200 C. and then it was kept at a temperature of 12001300 C. for an hour and was then cooled in order to cause Pb(Mg-W) O and PbTiO to react preferentially as described above. The cooled sintered ceramic was cut into a required size and its surface polished and then painted with silver on both surfaces of the piece, .fired at 600 C., and electrodes at tached.

The Curie point and the dielectric properties are measured by the use of this sample. In the measurement of the electromechanical properties, the polarization is performed by a direct current electric field of 40 kv./cm. within a silicone oil of a temperature of C. This con dition is the polarization condition for enlarging the electromechanical coupling coefiicient. On the other hand, in order to enlarge the mechanical Qm in general, the polarization is ordinarily performed under a low temperature and a high electric field such as, for example, 60 C. and 50 kv./cm. but the three component piezoelectric ceramic of our invention is such that the mechanical Qm can be enlarged by enlarging the polarization.

FIG. 4 shows that the planar coupling factor (kp) obtained exceeded 40%. In the present embodiment, kp was 50% and Qm was 200. As described above, the three component piezoelectric ceramic of Pb(Mg-W) O PbTiO and PbZrO in accordance with our invention exhibits excellent piezoelectric properties, and it became evident that it is a novel piezoelectric substance having excellent characteristics as an electromechanical transducer.

Furthermore, the crystal phase shown in FIG. 3 has the perovskite-type structure and can be divided into the tetragonal phase and the rhombohedral phase and exhibits a strong piezoelectric property. Said crystal system also has a pseudo-cubic section, but this is an area that can be utilized satisfactorily as the piezoelectric substance.

FIG. 5 shows an example of the dielectric properties of our invention. It is seen that notable peaks of dielectric constants are formed at the Curie points.

FIG. 6 shows the distribution in the three phase diagram of the Curie point and the distribution of the di electric constant measured at 20 C. and in 1 kc. Sometimes, 10 is exceeded.

Table 2 shows an example of the lattice parameters in each composition.

TABLE 4 Electro-mechanical properties Temperature I change in Additive, percent by weight Firin Mechan- Coupling resonant Basic composition, temp Density. ical, factor kp, frequency, No. 11101. F0203 C130 M1102 Others g./cm. Qm percent 17- Te 1 Pb(Mg-W)1 O 0.1 1,250 7.3 295 39 2. PbTiO 0.5 1,250 7. 6 500 39 X10- 3 PbZrOa 0.4 1, 250 7. 6 600 32 3Xl0- 4 1, 240 7. 5 90 60 1X10" 5 Pb(Mg-W)1/2O 0.1 250 7. 5 318 52. 3 6 10- 6 PbTiO3, 0.48 250 7. 5 800 45 5 10- 7 PbZ1'O 0.42 1,240 7.4 100 55 -1 10- 8 Pb(l\/ Ig-W)1 O 0.1 1, 255 7. 3 300 o ngggigj 8g 1, 255 7. 5 475 as 10 .W), ,Q,, 0,12 1,250 7.4 300 1 10- 11 PbTiOg, 0.48 1,250 7. 5 835 33 +8X10- 12 PbZrO 0.40 250 7. 5 831 +6X10- 1, 250 7. 5 1, 015 37 -6 10= 1, 245 7. 4 92 58 1X10- 250 7. 6 909 48 +4: 10- 1 250 7. 6 915 35 +1 10-- 250 7. 6 1, 200 45 5 10 1, 245 7. 4 97 58 1X10- 19 Pb(Mg-W)l/203, 0.15 1, 245 7.3 300 -8X10 20 PbTiO 0.45 1,245 7.6 850 47 -6X10 21 PbZrO 0.40 1.0 1,245 7.6 900 42 -7) 1()-s 22 1.0 1, 245 7.6 333 53 --s 10s 23 0. 3 0. 5 1, 245 7. 6 1, 315 41 -3 10s 24 Lazoa, 0.5 1,240 7.4 83 53 -1 10- 25 PbUMg-Wh/zOa, 0.2 0.2 1, 235 7. 4 300 51 1X10- 2e $12382 1, 235 7. 3 s7 51 2 10+ 27 rbnvr -wmoa, 0.35 1,210 7. 3 100 +4X10- 2s 9,1 ,32, 8? 8:23 1, 210 7. 4 300 48 3 10+ Pb(Mg-W)11z0g, 0.5 20 PbTiO 0.3 1 200 6.8 202 12 PbZ1O3, 0.2 so nggg gf glg 1,150 6.9 270 18 31.. Pb(Mg-w)1 O 0.15 1, 245 7. 5 1, 300 36 +7X10- 32 PbTiO 0.40 1, 245 7. 5 900 35 -5 10 1,245 7. 5 900 35 +3 10- 1, 240 7. 4 75 59 1 10- FIG. 7 is a triangular composition diagram showing the distribution of the electromechanical coupling coefiicient of the ceramic of our invention to which Fe O 40 and MnO have been added. This diagram shows that the state of distribution varies sightly depending on the additives. When MnO is added, Pb(Mg-W) O of 0.13 mol, PbTiO of 0.45 mol and PbZrO of 0.42 mol are the maximum and when Fe O is added, 0.13 mol/ 0.47 mol/ 0.40 mol is the maximum. Here, the area in the triangular composition diagram in which the electromechanical property is excellent is included in BCKJIHB of FIG. 2.

Furthermore, as to the eflfect given by the resonance frequency to the temperature characteristic, the addition of Cr O greatly improves the temperature characteristic. 5

However, La O and Nb O cannot give such eflect.

As evident from the above explanation of the details of this invention, the three component piezoelectric ceramic of Pb(Mg-W) PbTiO and PbZrO exhibits a completely new excellent electromechanical property and it will be evident that various kinds of piezoelectric transducers using this material can exhibit a greatly improved characteristic.

We claim:

1. A three component piezoelectric ceramic composition (Pb(Mg-W O (PbTiO) and (PbZrO having a composition within the range contained in polygon ABCDEFGA in the triangular composition diagram shown in FIG. 2 wherein Pb (Mg- W) i zOa PbTiOa PbZl03 0. 05 0. 15 0. 80 0. 05 0. 35 0. 60 0. 05 0. 55 0. 40 0. 05 0. 80 0. 15 0. 10 0. 80 0. l0 0. 80 0. 10 0. 10 0. 10 O. 10 O. 80 0. 05 0. 15 0. 80

and containing as additives at least one member of the group consisting of iron oxide, chromium oxide manganese oxide, lanthanum oxide and niobium oxide in an amount of from 0.1 to 2% by weight together with 0.02 to 0.5% by weight of silicon dioxide.

2. An electromechanical filter element manufactured from the three component system piezoelectric ceramic composition of (Pb(Mg-W) O (PbTiO and (PbZrO having a composition within the range 5 contained in polygon BCKJIHB in the triangular composition diagram shown in FIG. 2 wherein Pb(Mg-W) zO3 PbTiO PbZrO and containing as additives at least one member of the- U.S. Cl. X.R. 

